<p>Guanidinoacetate methyltransferase (GAMT) catalyses the last step of creatine biosynthesis. In humans, GAMT is believed to be the major enzyme involved in the metabolic conversion of S-adenosylmethionine (SAM) to S-adenosylhomocycteine (SAH). GAMT is found in abundance in the liver of all vertebrates. The crystal structure of a truncated version of GAMT shows that it exists as a dimer [<cite idref="PUB00035937"/>], and the structure can be viewed as a ternary complex between protein arginine methyltransferase (one subunit) complexed with a protein substrate (the partner subunit) and the product SAH. Deficiency of GAMT in the liver causes a hereditary disease with extra pyramidal motor disorder and extremely low concentrations of creatine in the brain, serum and urine [<cite idref="PUB00035938"/>].</p> <p>For additional information please see [<cite idref="PUB00028831"/>].</p>